Toni Bambang Romijarso, a doctoral student from the Department of Metallurgical and Materials Engineering, Faculty of Engineering, Universitas Indonesia (FTUI), completed his studies with a GPA of 3.96, earning the distinction of Cum Laude. Toni is the 74th Doctor from the Department of Metallurgical and Materials Engineering and the 568th Doctor at FTUI. His doctoral research focused on optimizing the martensite volume fraction in JIS G.3125 steel through intercritical annealing heat treatment at 750°C to meet the demands of the modern automotive industry.
“The automotive industry is always looking for materials that can provide a balance between strength, ductility, and fuel efficiency. Therefore, dual-phase steel has been a material of choice for a long time in the automotive industry to produce lighter yet still safe vehicles. The use of dual-phase steel directly contributes to fuel efficiency and reducing exhaust emissions, which is a major concern in the era of environmentally friendly vehicles,” explained Toni during his doctoral defence (03/09).
Toni’s research delved into optimizing dual-phase steel through heat treatment processes. Dual-phase steel consists of two phases, ductile ferrite and hard martensite, providing the perfect balance between strength and flexibility. In his study, Toni heated test samples to reach austenitization temperatures at various degrees—900°C, 920°C, 960°C, and 1000°C—holding for 30 minutes before quenching in water to form the martensitic phase. The material was then subjected to intercritical annealing at 750°C for varying hold times and subsequently water-quenched at room temperature, producing a dual-phase microstructure consisting of ferrite and martensite.
The study found that austenitization temperature and holding time during the intercritical annealing process significantly affect the microstructure size and shape of martensite. Higher austenitization temperatures resulted in coarser martensite grains, while longer holding times reduced the amount of martensite. The research also provided deep insights into controlling the mechanical properties of dual-phase steel, which directly impacts vehicle performance. The empirical equations derived from this study help predict mechanical properties based on the martensite volume fraction, enabling the industry to optimize steel according to its needs.
Toni’s research provides valuable insights into optimizing dual-phase steel by manipulating heat treatment processes, offering innovative solutions for the automotive industry, which requires lightweight, strong, yet safe and environmentally friendly materials. “Dr. Toni Bambang’s research contributes significantly not only to scientific development but also directly to the automotive industry. The use of dual-phase steel to reduce vehicle weight not only increases fuel efficiency but also helps reduce exhaust emissions. This is an important step in supporting the development of environmentally friendly vehicles, which are greatly needed in the future,” said Acting Dean of FTUI, Prof. Ir. Mahmud Sudibandriyo, M.Sc., Ph.D.
The results of the research were presented during the open doctoral defence chaired by Prof. Ir. Mahmud Sudibandriyo, M.Sc., Ph.D., as the Chair of the Examination, with Prof. Dr. Ir. Eddy Sumarno Siradj, M.Sc. Eng. as the Promoter, and Prof. Dr. Efendi, S.T., M.T., and Prof. Dr. Ir. Myrna Ariati Mochtar, M.Sc. as Co-Promoters. The examination board consisted of several experts, including Prof. Dr. Ir. Johny Wahyuadi, DEA., Prof. Dr. Ir. Winarto, M.Sc., Dr. Deni Ferdian, S.T., M.Sc., Drs. Nofrijon Sofyan, M.Si., Ph.D., and Dr. Ahmad Zakiyuddin, S.T., M.Eng.
Through his dissertation, Dr. Toni Bambang has demonstrated how dual-phase steel can be further developed to support the automotive industry. By understanding the relationship between temperature and holding time, it is hoped that the automotive industry can optimize the mechanical properties of steel according to specific application needs.
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Faculty of Engineering, Universitas Indonesia
